Method and device for sorting products according to emitted light

ABSTRACT

A method for sorting products including the steps of conveying the products in a product stream, scanning the products in the product stream casting light onto the products on the basis that certain products will emit light, observing emitted light from the products, making a selection of certain products from the product stream as a function of the observed light, and separating certain products from the product stream as a function of the selection. A device is provided that is arranged to sort the products according to the method of the invention and includes a light device that is arranged to cast light onto products and an observation device that is arranged to observe light emitted from the products. A selection device is also provided that is arranged to make a selection of whether to separate certain products from the product stream observed by the observation device.

BACKGROUND OF THE INVENTION

The present invention concerns a method and a device for sortingproducts.

It is meant in particular for removing certain products from a productstream.

In particular, it aims a method and a device which is very suitable tobe applied in the food industry, for example for sorting out non-foodproducts from certain foods, in particular leaves, branches and piecesof waste such as wood, plastic, stones, etc.

However, the products to be sorted can also be foods of differentquality, whereby a quality selection is made by means of the sorting.The method can also be used to separate good and bad products.

It is known from the international patent application WO 96/00621 toilluminate the products to be sorted with a light beam and tosubsequently carry out a selection on the basis of the light which iscollected by means of reflection, fluorescence or such. The collectedlight is treated in a spectroscopic analysis device which delivers anoutput signal for the selection as a function of the analysis. As use ismade of a spectral analysis, whereby the entire spectrum has to beanalysed every time, this system is very expensive since it requires aspectroscopic analysis device.

A method is known from the international patent application WO 97/42489to determine the ripeness of seeds by means of the fluorescence of thechlorophyll in the seeds, after they have been illuminated. Thedescribed method makes it possible to shine light through the seeds oneafter the other, but it does not offer a practical embodiment for thetreatment of large amounts at once. Moreover, the described method onlyleads to a selection among seeds, but it does not go in the direction ofselecting strange products from foodstuff or such.

A method for sorting particles is known from the patent application GB2.292.455, whereby the particles to be sorted are irradiated with alaser and the obtained ‘Raman scattering’ is used as a sortingcriterion. As exposed in GB 2.292.455, normal Raman scattering isdisadvantageous in that the signal obtained by means of ‘scattering’ isdisturbed too much by the ‘emission’ obtained by means of fluorescence,and thus becomes difficult to detect. That is why it is suggested in GB2.292.455 to make use of a stimulated Raman signal. However, thistechnique is in turn disadvantageous in that a high energy supply isnecessary, requiring expensive equipment.

BRIEF SUMMARY OF THE INVENTION

In general, the invention aims a method and a device which make itpossible to carry out a very efficient and reliable selection in a largeproduct stream, such that the sorting can be applied at an industriallevel for the treatment of large quantities of products.

In particular, according to a number of preferred embodiments, it aims amethod and a device whereby the use of expensive spectrographicalanalysis equipment is excluded, and whereby large quantities can betreated.

To this aim, the invention in the first place concerns a method forsorting products, characterised in that it at least consists inconveying the products to be sorted in the shape of a product stream,extending in the width, over a specific path; in scanning the productsto be sorted over the width of said product stream, by casting lightonto the products on the one hand, at least in a specific spectrum whichis selected such that certain products of the products to be selectedwill emit light, and by observing this light in a specific range of thespectrum in which the emitted light is cast on the other hand; in makinga selection between the scanned products as a function of the observedlight; and in automatically separating the products from theabove-mentioned product stream as a function of said selection.

By making use of a wide product stream which is scanned over the widthon the one hand, and by making use of emitted light on the other hand,it is possible to make a particularly fast and efficient selection withgreat certainty and with a minimum of faults, such as opposed to forexample the above-mentioned known systems, as well as the systems whichare available on the market, whereby the selection is exclusively madeon the basis of reflected light, in particular by means of colourrecognition.

By making use of a spontaneous ‘emission’, by which is mainly implied‘fluorescence’ as will be further explained, the effect which is felt asbeing disadvantageous according to GB 2.292.455, will be used as anessential characteristic according to the invention to carry out theselection. This effect is particularly useful when sorting specificfoods, whereby Raman scattering does not offer an efficient solution.

Preferably, in order to observe the light which is emitted by theproducts concerned, use is made of an optical filtering, in particularby means of an optically adjusted filter, for example a band-passfilter. This allows for an almost instant evaluation and selection ofthe scanned products, as opposed to the relatively complicated andexpensive spectral analysis which is applied in the method described inWO 96/00621.

The selection is preferably made on the basis of a certain intensityvalue of the emitted light or of a signal corresponding to it beingeither exceeded or just not exceeded. As use is made of the emission ina specific spectrum, there is a very clear distinction between signalswhich are related to a light-emitting product and signal which arerelated to a non-light-emitting product, which makes it possible to makea very efficient distinction by simply verifying whether the signalseither or not exceed a certain value.

In particular, the light is preferably cast from such a part of thespectrum that light is emitted by the products concerned in another partof the spectrum. This makes it easy to make a distinction between theemitted light and possibly directly reflected light by means of anoptical band-pass filter or such.

According to the most practical embodiment according to the invention,use is made of the fluorescence qualities for the emission, inparticular the fact that the scanned products either or not fluoresce.

More in particular, the method will be used for sortingchlorophyll-containing foods, in particular for the selection of strangeproducts from foods.

The invention is particularly useful for separating waste from forexample peas, especially for separating strange products therefrom suchas stones, pieces of wood, plastic and such.

In the case where the method is applied for separating waste fromproducts containing chlorophyll, such as for example peas, light ispreferably emitted during the scanning having a wavelength in the orderof magnitude of 640 to 680 nanometer, whereas other light is preferablyexcluded. Thus, only the foods containing chlorophyll, in this case thepeas, start to emit light in the spectrum to be observed as a result offluorescence. This wavelength selection can also be used for other foodscontaining chlorophyll, such as beans, lettuce, sprouts, etc.

In order to observe the emitted light, observations are preferablyexclusively made in the wavelength range of 690 to 740 nanometer,preferably by means of optical filtering, and in particular in a rangewhich has a value in the order of magnitude of some 715 nanometer. Inthis range, the emission can be optimally observed.

According to another application of the invention, use is made for theemission of the light-emitting quality of certain organisms such asbacteria, fungi and such, which can be found on certain products,whereby a selection is made between the products on the basis of saidemission.

A practical application thereof according to the invention consists insorting foods which are affected by fungi from non-affected foods, inparticular in sorting nuts or figs which are affected by aflatoxins.Preferably, there will be an excitation with deep blue UV light (340 to400 nm). The observed emitted light will then be green. Preferably,measurements will only be carried out in the wavelength range of 440 to550 nm in this case.

According to a major variant of the invention, use is made of abackground which will emit light when it is being illuminated, inparticular which will fluoresce, such that the light being cast willalso produce an emission effect in those places where it is not cast ona product. This offers the advantage that it becomes possible to make asimple selection between light-emitting and non-light-emitting productswithout any special measures being required to prevent that those placeswhere there is no product and which are observed during the scanning areregarded as places where strange products to be removed are found.

Use is preferably made here of an emitting background of a surfaceextending in the width of the product stream which is spherical on theside where the light is cast upon. The spherical shape promotes a veryprecise emission.

Practically, the above-mentioned background will consist of acylindrical roller.

According to a special embodiment, instead of using a background whichemits light after light has thus been cast upon it, use can also be madeof a background which constantly emits light, preferably of a wavelengthwhich is ideal in relation to the selection to be made.

As for the emitting background, a background is preferably providedwhich emits light having a wavelength of the same order of magnitude asthe light which is emitted by the products to be treated.

In order to be able to obtain high emission values with a minimum ofenergy, and consequently to be able to make observations with greatcertainty, the scanning according to the invention is preferably carriedout by means of a laser, in particular by making a laser beam movediagonally over the product stream in a systematic manner.

According to a very advantageous embodiment, a scanning system with amoving mirror, preferably a rotating polygon mirror or another opticalelement is used, and the emitted light is returned via the same mirroror the same optical element.

Instead of making use of a laser, the scanning can also take place inanother way, for example by means of a fixed light band or a series oflight points, directed onto the products which pass by over the width ofthe product stream, whereby at least the emitted light is observed bymeans of a camera, and whereby the selection is made on the basis of theevaluation of camera images.

In order to make the products move in the shape of a product stream witha certain width along the place where they are scanned, use can be madeof different techniques. A practical technique consists in bringing theproducts in a single plane on the place where they are to be scanned,via a table, belt or such, either or not provided with longitudinalducts or grooves.

Further, the products preferably fall down freely and the products to beseparated are moved apart by means of nozzles which are erected over thewidth of the product stream and which are individually activated as afunction of the observations made, whereby for example the products tobe removed from the global product stream are blown away and arecollected in a recipient.

In order to further optimise the method, the products to be sorted canbe scanned from two sides, situated opposite to the product stream. Thismakes it possible to make a right selection with more certainty, whichis particularly important when there is a possibility that products showdifferent qualities on the front and on the back side.

It should be noted that the method of the invention can possibly becombined with another scanning process, for example with a coloursorting by means of the reflected light. In the latter case, differentlaser beams can be used, namely at least one laser beam to realise theabove-mentioned emission in a different spectrum, and at least one laserbeam for sorting for example on the basis of the normal lightreflection. Practically, the different laser beams can then besimultaneously guided along the same light path according to theinvention, possibly slightly shifted in relation to one another. As aresult, only one polygon mirror or another optical element will berequired to move the laser beams over the product stream.

Apart from the above-mentioned method, the invention also concerns adevice for sorting products according to the method, characterised inthat it at least consists of the combination of means for conveying theproducts to be sorted-in the shape of a product stream extending in thewidth over a certain path; means for scanning the products to be sortedover the width of said product stream, consisting of means to cast lighton the products on the one hand, at least in a specific spectrum whichis selected such that specific products to be sorted will emit light,and of means to observe this light in a specific range of the spectrumin which the cast light is emitted, on the other hand; means to make aselection between the scanned products as a function of the observedlight; and means to automatically separate the products from theabove-mentioned product stream as a function of said selection.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to better explain the characteristics of the invention, thefollowing preferred embodiments are described as an example only withoutbeing limitative in any way, with reference to the accompanyingdrawings, in which:

FIG. 1 schematically illustrates the method according to the invention;

FIG. 2 represents an example of a signal which is obtained during thescanning of the products concerned;

FIG. 3 represents a device according to the invention in perspective;

FIG. 4 schematically represents the device of FIG. 3;

FIG. 5 represents a section according to line V—V in FIG. 4;

FIG. 6 schematically represents a section according to line VI—VI inFIG. 5;

FIG. 7 schematically represents a variant of a device according to theinvention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 schematically represents how the products 1-2 to be sorted areconveyed over a certain path 3 in the shape of a product stream 4 whichextends in the width, in particular a certain width B. The products 1-2are hereby schematically represented as good products 1, for examplepeas or other products containing chlorophyll, and the products 2 to beremoved, for example strange elements such as stones, pieces of wood andplastic.

According to the invention, the product stream 4 is scanned by castinglight 6 on the products 1-2 with the help of appropriate means 5 on theone hand, at least in a specific spectrum which is selected such thatspecific products to be sorted, in this case the products 1, emit light7, whereas the other products 2 don't, and by observing the light 7 withthe help of appropriate means 8 in a specific range of the spectrum inwhich the emitted light 7 is emitted on the other hand.

The means 5 hereby consist of a light source 9, preferably a laser whichemits the light 6 in the shape of a ray of light, namely a laser beam10, as well as means to systematically turn the laser beam 10 over anangle A which are not represented here, such that the product stream isscanned over the width B, in particular on the place of the line part L.

The means 8 consist of an optical filter 11 on the one hand which mainlyexclusively lets the light 7 through from the spectrum range in whichthe emission takes place, and of a detection device 12 to observe saidlight 7 on the other hand.

Further, FIG. 1 schematically represents means 13, such as an electronicprocessing unit, to make a selection between the scanned products 1-2 asa function of the observed light 7, also as a function of the place onthe line part L where said light 7 came from.

In order to automatically separate the products 1 and 2, means 14 areprovided which in this case consist of nozzles 15 which can beindividually activated and which are controlled by means of a valve unit16 which is not further described here, as a function of the signals 17coming from the above-mentioned processing unit. The means 14 alsocomprise a partition 18.

It is clear that the necessary means are further provided to separatethe cast light 6 and the emitted light 7 in an appropriate manner, forexample by means of a semi-transparent mirror 19, as is schematicallyrepresented.

Finally, another element 20 is represented in FIG. 1 having a surface 21which forms an emitting background. As explained in the introduction, itpreferably consists of a cylindrical roller.

The method according to the invention consists in that light 6 is casthaving at least such a wavelength that one of either products 1-2, whenit is irradiated by the light 6, spontaneously starts to cast or emitlight at another wavelength than that of the light 6 with which it isirradiated.

In the case where the products 1 consist of peas or other productscontaining chlorophyll, in particular foods, light 6 from the spectrumof 690 to 740 nanometer will be cast.

As a result thereof is obtained that when the laser beam 10 hits aproduct 1, in particular a pea, light 7 is emitted. The same occurs whenthe laser beam 10 hits no product 1 or 2 whatsoever, whereby in thiscase light having practically the same wavelength is emitted due to thefluorescence of the surface 21.

If, however, the laser beam 10 hits a product 2, such as a stone orsuch, there will be no fluorescence, and hence no light 7 will beemitted.

By moving the laser beam 10 at a sufficiently high speed over the widthB, for example at 12,000 cycles per minute, all products 1-2, which falldown freely in the given example, can be scanned without any problems.

As a result, light 7 is observed which, after being transformed, resultsin an electric signal E, such as represented for example in the diagramof FIG. 2, whereby this signal is measured out as a function of theabove-mentioned width B. The parts 22 of the signal progress are herebythe result of the emission occurring with a product 1, in particular apea, whereas the parts 23 are the result of the emission at the surface21. The parts 24 indicate that products 2 are present which cause noemission.

Subsequently, in the means 13 forming the processing unit, an automaticselection is carried out to detect the places where the products 2 pass,on the basis of the above-mentioned signal progress. As explained in theintroduction, this is preferably done on the basis of a certain value ofthe above-mentioned signal being either or not exceeded, in particularby checking when the signal goes beneath a certain limit value W in thecase of FIG. 2. It is clear that, each time the signal goes beneath saidvalue W, this means that a product 2 is being observed.

In order to efficiently remove the products 2, one or several nozzles 15are activated, on the place where the product 2 is found, so that eachsuch product 2 is blown out of the product stream 4, in particularbehind the partition 18. As they are blown away, it may happen that anumber of products 1 are also removed from the product stream 4, butsince the quantity of products 2 usually is very small in relation tothe quantity of products 1, also the good products 1 which are blown outof the product stream 4 will be limited in number.

FIGS. 3 to 6 hereafter represent a possible practical construction of adevice 25 for realising the above-mentioned method in further detail.

FIG. 3 shows the device 25 as a whole. This device 25 is equipped withtwo optical units 26 and 27 which, as is schematically represented inFIGS. 4 and 5, make it possible for the products 1-2 to be scanned oneither side. Every unit 26, 27 respectively, has a construction as isschematically represented in FIG. 1, as well as in FIG. 6 which will bedescribed hereafter.

In order to carry the products 1-2 in the shape of a product stream 4with a certain width but with a small thickness past the place wherethey are scanned, a device 25 is equipped with means 28 in the shape ofa vibrating table 29, from where the products 1-2 are vibrated downwardover the edge 30 of this vibrating table 29. Via a sliding surface 31they are guided into a zone 32, where they fall down freely and wherethey are also scanned, as mentioned above.

The products 1 which have been let through are guided further via adischarge chute 33, whereas the removed products 2 are collected in arecipient 34 or such.

It is clear that, according to a variant, instead of a vibrating table29, use can also be made of a conveyor belt or such. Also longitudinalducts or grooves can be provided in the vibrating table to obtaindifferent parallel rows of products 1-2 falling down, whereby forexample each row passes exactly one nozzle 15.

FIG. 6 further schematically represents how the cast light 6 and theemitted light 7 which is caught again by means of a moving mirror 35, inparticular a rotating polygon mirror, can be moved over the width B ofthe product stream 4.

FIG. 7 represents a part of a special embodiment of a device 25according to the invention. The means for conveying the products 1-2 tobe sorted in the shape of a product stream 4 over a certain path herebymainly consist of a drum 36 which is provided with inlets 37 on itssurface against which the products 1-2 are sucked, by creating a vacuumin an appropriate manner. The means for automatically making aseparation as a function of the selection in this case consist of meanswhich are not represented, in particular valves or such, which make itpossible to selectively control the inlets 37 concerned, in particularto close or to open them.

The working is then mainly as follows: the product stream 4 is forexample brought into contact with the surface of the drum 36 via a feedchute 38. Thanks to the suction force on the inlets 37, products 1-2 aresucked onto the surface of the drum 36, as a result of which the productstream 4 so to say continues on the surface of this drum 36.

Then, the products 1-2 are scanned by means of an optical unit 39,analogous to that of the preceding embodiment.

The surface of the drum 36 may hereby either or not consist of alight-emitting material, with the same purpose as the surface 21 of theabove-mentioned element 20.

By providing two ducts 40 and 41 for the separate discharge of theproducts 1-2 and by interrupting the sucking action on the respectiveinlets 37 as a function of the data obtained by means of the scanning,it is possible to carry out a separation. Above the duct 41, the inlets37 holding products 2 are closed, such that the sucking action isinterrupted and that these products 2 fall in the duct 41. Above theduct 40, the suction action of all inlets 37 is interrupted, such thatall the products 1 there come loose of the drum 36.

It should be noted that, as opposed to what is schematically representedin FIGS. 1 and 4 to 7, the width B is in reality a considerable numberof times the diameter of the product 1-2. In reality, this width willusually be in the order of magnitude of 0.3 to 1 meter, but of course itcan also deviate therefrom. Further, the product stream 4 in realityconsists of a quantity of products 1-2 spread out over almost the entiresurface of the path 3.

The invention is by no means limited to the above-described embodimentsrepresented in the accompanying drawings; on the contrary, such a methodand device can be made in all sorts of variants while still remainingwithin the scope of the invention.

What is claimed is:
 1. A method for sorting products, comprising thesteps of: conveying the products to be sorted in the shape of a productstream extending in a path width over a specific stream path; scanningthe products to be sorted over the path width f said product stream bycasting light onto the products and onto a background element with afluorescent surface, at least in a specific spectrum which is selectedon the basis that certain products of the products to be selected andthe fluorescent background will emit light; observing the emitted lightin a specific range of the spectrum in which the light is emitted;making a selection between the scanned products as a function of theobserved light; and automatically separating the products from theabove-mentioned product stream as a function of said selection.
 2. Themethod according to claim 1, wherein optical filtering-by means of anoptically adjusted filter is used to observe the light emitted by theproducts.
 3. The method according to claim 1, wherein the selection ismade on the basis of reaching a certain intensity value of the emittedlight or of exceeding a signal corresponding to the emitted light. 4.The method according to claim 1, wherein light is cast from such a partof the spectrum that light from another part of the spectrum will beemitted from the products concerned.
 5. The method according to claim 4,wherein use is made of fluorescence qualities for the emission so as todetermine whether the scanned products fluoresce.
 6. The methodaccording to claim 1, further comprising the step of sortingchlorophyll-containing foods to distinguish non-food products from thefood products.
 7. The method according to claim 6, further comprisingthe step of selecting waste from peas.
 8. The method according to claim1, wherein light is emitted during the scanning and has a wavelength onthe order of magnitude of 640 to 680 nanometers.
 9. The method accordingto claim 1, wherein the observed emitted light is in a range which has avalue on the order of magnitude of 715 nanometers.
 10. The methodaccording to claim 1, wherein the light-emitting quality of certainorganisms is used as a criteria for the selection of the products. 11.The method according to claim 10, wherein the sorted products are nutsaffected by aflatoxins and nuts not affected by aflatoxins.
 12. Themethod according to claim 1, wherein the observed emitted light iswithin the spectral range of 690 to 740 nanometers.
 13. The methodaccording to claim 1, wherein the background is a surface that extendsalong the path width of the product stream and spherical on the sidewhere the light is cast upon.
 14. The method according to claim 13,wherein the background comprises an element in the shape of acylindrical roller.
 15. The method according to claim 1, wherein thebackground is configured to constantly emit light.
 16. The methodaccording to claim 1, wherein an emitting background is provided andemits light having a wavelength of the same order of magnitude as thelight which is emitted by the products to be treated.
 17. The methodaccording to claim 1, wherein a laser is used to scan the products. 18.The method according to claim 17, wherein the step of scanning includesmoving a laser beam diagonally over the product stream in a systematicmanner.
 19. The method according to claim 18, wherein a scanning systemwith a rotating polygon mirror is provided to scan the produce stream,and the emitted light is returned via the rotating polygon mirror. 20.The method according to claim 1, wherein the scanning takes place bymeans of a fixed light band or a series of light points directed ontothe products which pass by over the width of the product stream, wherebyat least the emitted light is observed by a camera.
 21. The methodaccording to claim 1, wherein the products are brought in a single planeon the place where they are to be scanned via a table.
 22. The methodaccording to claim 21, wherein the table vibrates and is provided withlongitudinal grooves or ducts.
 23. The method according to claim 1,wherein the products to be sorted are scanned from two sides, situatedopposite to the product stream.
 24. The method according to claim 1,further comprising the step of sorting the products on the basis oflight reflection.
 25. The method according to claim 24, whereindifferent laser beams are used and simultaneously guided along a samelight path.
 26. The method according to claim 25, wherein the differentlaser beams are shifted in relation to one another.
 27. The methodaccording to claim 1, wherein the products fall down freely and theproducts to be separated are moved apart by means of nozzles erectedover the width of the product stream and activated individually or ingroups as a function of the observed emitted light.
 28. A device forsorting products, comprising: a conveying device arranged to convey theproducts to be sorted in the shape of a product stream extending in thepath width over a certain path; at least one background element with afluorescent surface; a scanning device arranged to scan products to besorted over the path width of said product stream including a lightdevice configured and arranged to cast light on the products and on thebackground in at least a specific spectrum selected such that specificproducts to be sorted and the background will emit light, and anobservation device configured to observe the light in a specific rangeof the spectrum in which the light is emitted; a selection deviceconfigured and arranged to make a selection between the scanned productsbased on a selection criteria as a function of the observed light; and aseparation device configured and arranged to automatically separate theproducts from the product stream on the basis of the selection criteria.29. The device according to claim 28, wherein the light device includesa laser generating a laser beam and an optical device arranged andconfigured to make the laser beam move in the path width over theproduct stream.
 30. The device according to claim 28, wherein theobservation device includes an optical collector arranged and configuredto collect the emitted light and guide it to the selection device forcarrying out the selection, the optical collector having an opticallyadjusted filter.
 31. The device according to claim 28, wherein theconveying device includes a vibrating table upon which the products areplaced and are subsequently vibrated away over an edge thereof.
 32. Thedevice according to claim 28, wherein the separation device includes aseries of nozzles activated as a function of the selection criteria andthe separation to be realised.
 33. The device according to claim 28,wherein the conveying device includes a drum provided with inlets on itssurface against which the products are sucked, and in that theseparation device includes a selection device arranged and configured toselectively control the inlets.
 34. The device according to claim 28,wherein the scanning device includes at least one element backgroundforming a light-emitting background.
 35. The device according to claim34, wherein the background element includes a cylindrical roller.